Structure and Properties of Amino Acids and Proteins

Amino AcidsGeneral Features

Isomerism, Chirality and Optical RotationAmphoteric PropertiesAmino Acid Side ChainsAcid Base Characteristics of Amino Acids

Peptides and ProteinsLevels of Protein Structure

Primary StructureSecondary StructureTertiary and Quaternary Structures

How Protein Conformations are Stabilizing

General Amino Acid Structure

General Amino Acid Features

-O OC

R

+H3N HC

= O O-C

R

NH3+H C

=

L - isomer D - isomer

Isomerism

Constitutional isomers, nonsuperimposable, mirror images(i.e. stereoisomers)

General Amino Acid Features

-O OC

R

+H3N HC

= O O-C

R

NH3+H C

=

R - clockwise

Chirality and the R, S system

S - counterclockwise

H < C < N < O

General Amino Acid Features

-O OC

R

+H3N HC

= O O-C

R

NH3+H C

=

L - isomer D - isomer

Amphoteric Properties

Zwitterions

ValineAlanine

Pyruvate

Nonpolar Hydrophobic Amino Acids

Isoleucine Leucine

Proline

Phenylalanine

Tryptophan

Tyrosine

Aromatic Amino Acids

Aspartic AcidOxaloacetate

Glutamic AcidA-ketoglutarate

Metabolic intermediatesMetabolic intermediates

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HistidineArginine

Lysine

Positively Charged Amino Acids

Threonine

Asparagine

Methionine

SerineCysteine

Glutamine

Amino Acids with Uncharged R- groups (but vary in polarity)

Glycine

Essential amino acids

1. Humans can produce 10 of the 20 amino acids. The others must be supplied in the food. 2. Failure to obtain enough of even 1 of the 10 essential amino acids, those that we cannot

make, results in degradation cellular and noncellular proteins to obtain the one amino acid that is needed.

3. Unlike fat and starch, the human body does not store excess amino acids for later use—the amino acids must be in the food every day.

4. The 10 amino acids that we can produce are:

Alanine Asparagine Aspartic acid

Cysteine Glutamic acid Glutamine

Glycine Proline Serine

Tyrosine

Tyrosine is produced from phenylalanine, so if the diet is deficient in phenylalanine, tyrosine will be required as well.

Proline

The essential amino acids are:

Arginine Histidine Isoleucine

Leucine Lysine Methionine

Phenylalanine Threonine Tryptophan

Valine

These amino acids are REQUIRED in the diet.

They are INDISPENSABLE .

http://upload.wikimedia.org/wikipedia/commons/6/6d/Peptidformationball.svg